Magnetic inertia controlled fuze



Aug. 26, 1958 J. PLUMLEY MAGNETIC INERTIA CONTROLLED FUZE 2 Sheets-Sheet 2 Filed May 16, 1944 hvwv wv mv NW m hv mm mv mm n NN mm mm VN 2,848,948 MAGNET IC INERTIA CONTROLLED FUZE Harold J Plumley, Washington, D. C. Application May 16, 1944, Serial No. 535,799

14 Claims. (CI. 102-702) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to a magnetically controlled fuze for detonating an explosive charge, and more particularly to a fuze in which the firing is accomplished by sudden movement of an inertia. element sufficient to cause a change in the fiux within a magnetic circuit thereby to generate a voltage in a coiled disposed within the magnetic circuit and thereby fire a low energy detonating device.

In inertia controlled devices heretofore devised for firing an explosive 'charge, it has been the general practice to arrange the inertia element thereof in such a manner :that the element is adapted to be moved along a predetermined axis when the forward motion of the device is suddenly arrested and thereby cause a firing pin to be actuated and fire the cap, the inertia element being normally and yieldably retained in an initial position by a spring or shear element. Such devices, when employed with a projectile, for example, have not proved entirely satisfactory under all conditions of service for the reason that the friction developed by the lateral component of the set forward force applied thereto when the projectile strikes the target a glancing blow may be sufiicient to prevent the inertia element moving to a firing position and thus the projectile may fail to explode. Furthermore, when the projectile strikes a target comprising a relatively thin plate, the pulse transmitted to the firing plunger may be insuficient to cause firing of the percussion cap.

In the device of the present invention, the firing of the fuze is accomplished by sudden movement of a.magnetic keeper comprising the inertia element of the device with respect to the magnetic structure with which the keeper is normally engaged by reason of the provision of a strong permanent magnet Within the magnetic structure. The magnet is sufficiently strong to prevent disengagement of the keeper therefrom as the result of shocks received during the handling, transportation and loading of the projectile within the gun. The keeper is adapted to be disengaged from the magnetic structure by a set forward force applied along the axis of the projectile as the projectile strikes a target, or by a set forward force applied -to the projectile at an angle with respect to the axis thereof, and thus a sudden voltage is generated within a coil included within the magnetic structure suflicient to fire a low energy detonator or cap regardless of Whether the projectile strikes the target head on or strikes the target a glancing blow. The device of the present invention is adapted for a variety of uses other than as a means of firing a projectile as the projectile strikes a target and may be employed, for example, for firing a bomb or rocket, as the case may be. The device may also be employed for firing a glider bomb in which the bomb generally stn'kes the target a glancing blow and may also be used for firing anti-submarine projectiles.

For the purpose of description, the fuze of the present invention will be described in connection with a projectile in which the set back force as the projectile is fired is relatively high and in which the projectile performs the usual gyrations and nutations during the travel of the projectile along a trajectory.

One of the objects of 'the present invention is to provide a new and improved fuze adapted to be fired by a set forward force applied suddenly thereto along the axis of the fuze or at `an angle with respect thereto.

Another object is to provide a fuze for a projectile having means for detonating an electroresponsive cap by a voltage generated within the fuze as the rate of forward movement of the projectile is suddenly decreased.

Another object is to provide a new and improved magnetically controlled fuze adapted to be fired in response to an increase in the reluctance of the magnetic circuit as the rate of forward movement of the fuze is suddenly decreased.

Another object is to provide a new and improved fuze for a bomb in which the firing of the -bomb is delayed until the bomb has substantially come to rest after striking the target.

Another object is to provide a device for a fuze adapted to generate a voltage in response to a set forward force of predetermined value applied to a movable magnetic element in which means are provided for preventing the generation of a voltage when set forward forces of strength less than said predetermined value are applied to the magnetic element.

Still another object is to provide an inertia controlled firing device for an explosive charge which is economical to manufacture, reliable in operation and possesses all the qualities of ruggedness and dependability in service.

Still other objects, advantages and improvements will become apparent from a consideration of the following description taken in connection with the accompanying drawings, of which:

Fig. 1 is a View partly in elevation and partly in section of a projectile employing the device of the present invention;

Fig. 2 is a view taken along the line 2-2 of Fig. l;

Fig. 3 is a view taken along the line 3-3 of Fig. l;

Fig. 4 is an enlarged view partly in elevation and partly in section of the device according to a preferred embodiment of the invention;

Fig. 5 is a fragmentary sectional view showing the keeper disengaged from the core as the result of a set forward force applied axially thereto;

Fig. 6 is a fragmentary sectional view showing the keeper disengaged from the core as the result of a set forward force applied at an angle with respect to the axis thereof; and,

Fig. 7 shows in diagrammatic form an arrangement for firing the detonator in time delayed relation with respect to the instant of impact of the projectile against the target.

Referring now to the drawings for a more complete understanding of the invention and more particularly to Fig. 1 thereof, there is shown thereon an armor piercing projectile indicated generally by the numeral 10 having a body 11 to which is secured in any well known manner a rotating band 12. The projectile is also preferably provided with a cap 13 of relatively soft metal and a windshield 14 secured thereto as is well known in the art of armor piercing projectiles. The projectile body is provided with a recessed portion 15 having an explosive charge 16 therein and enclosed by a base plate 17 secured to the rear portion of the projectile. The base plate is preferably threaded to receive and support the fuze 18 in an inwardly extending position within the recessed portion 15 of the projectile body.

The fuze 18 comprises a body 19 preferably recessed to receive a tracer 21, as is well known in the art to which the present invention relates. As shown in Fig. 4, the body 19 has a bore therein adapted to receive an arming device comprising a sleeve 22 secured within the bore as by the screw 23. Slideably arranged within the sleeve 22 is a plunger 24 releasably locked in a safe position by a detent (not shown) within a recessed portion 25 formed therein. As the shell is fired, centrifugal force is applied thereto and causes the detent to be released and the plunger 24 to be moved within the sleeve 22 to an armed position with an explosive lead or train 26 therein in alinement with a pair of apertures 27 and 28 Within the sleeve. The sleeve 22 is secured to the fuze body with the apertures 27 and 28 thereof in substantial alinement with a pair of caps 29 and 31 respectively, the cap 29 being in operative relation with respect to an explosive booster charge 32 arranged within a transverse bore 33 within the fuze body and adapted to complete the explosive train between the cap 29 and the main explosive charge 16. The cap 31 is adapted to be fired by the electroresponsive detonating device 34 secured within the body of the fuze by the screw 35 and provided with a pair of electrical conductors 36 for establishing an external control connection thereto. v

The fuze body 19 is also provided with a sleeve 37 arranged exteriorly thercon and adapted to protect the arming mechanism and prevent the main explosive charge from coming into contact with the arming mechanism including the plunger 24. The fuze body 19 s also preferably recessed to receive and support a safety switch 38 adapted to short-circuit the conductors 36 until the projectile has been fired, the switch comprising an actuating member adapted to disengage the contact elements thereof in response to the centrifugal force applied thereto as the projectile is fired. The switch may be of any well known type suitable for the purpose in which means are provided for short circuiting the detonator 34 at all times prior to the firing of the projectile and in which the short circuit is removed during the flight of the projectile along a trajectory.

Secured to the fuze body 19 as by the nut 39 is the voltage generating device of the present invention, the device comprising a core 41 composed of magnetic material and having an enlarged head 42 adapted to be clamped in abutting relation with the end of the fuze body 19, a pair of dowel pins 43 being preferably provided to maintain the core in registered engagement with the fuze body as the nut 39 is tightened. The nut 39 is composed of nonmagnetic material suitable for the purpose. comprising a large number of turns of wire to which the conductors 36 are connected, an aperture 45 being provided within the head of the core to permit an electrical connection to be established to the coil.

There is also arranged about the coil 44 and in abutting relation with the head of the core 41 a circular magnet 46 adapted to be engaged by the nut 39 as at 47 whereby the magnet and core are secured to one another and to the fuze body 19 in predetermined spaced relation as the nut 39 is tightened. An arrangement is thus provided in Which the outer ends of the magnet 46 and the core 41 are drawn into a single plane. An inertia member or keeper 48 composed of magnetic material is adapted to engage the outer ends of the magnet and core thereby closing a magnetic circuit of low reluctance at all times except when the keeper is dislodged from engagement with the core as the fuze receives a set forward force of predetermined strength.

The keeper 48 is disposed within a cap or easing 49 composed of nonmagnetic material and having a recessed portion or well 51 therein of sufficient size to permit the keeper to be moved away from the core 41 in response to a predetermined degree of set forward force applied to the keeper.

Whereas in the illustrated embodiment of the invention, the keeper 48 is shown as a truncated cone, it will of course be understood that, if desired, the keeper may be of various shapes and sizes in accordance with the sensitivity of response of the device to a set forward force applied thereto. In the case where the set forward The core 41 is also provided with a coil 44 force is applied substantially along the axis of the core 41, the sensitivity of response of the device is controlled generally by the mass of the keeper, and in the case Where the set forward force applied thereto comprises a substantial component of force in a direction normal to the axis of the core, the sensitivity of response of the device is controlled by the mass of the keeper and the distance of the .center of gravity thereof from the face of the keeper in engagement with the core.

On Fig. 5 is shown the inertia member or keeper 48 in engagement with the bottom of the well 51 and disengaged from the core 41 by the set forward force applied to the fuze as the projectile strikes the target substantially head on. The magnet 46, it will be noted, is of sufiicient strength to cause the keeper 48 to be drawn into contact with the core 41 and with one end of the magnet when the set forward force applied to the keeper has been expended. An arrangement is thus provided in which the keeper 48 is in engagement with the core and the magnet at all times except when a set forward force of predetermined strength is applied to the keeper.

On Fig. 6 is shown the keeper 48 moved out of engagement with the core 41 as the result of a set forward force applied to the keeper at a substantial angle with respect to the axis of the core, the keeper being tilted into engagement with the bottom portion and the side wall of the well 51 respectively.

An arrangement is thus provided in which the keeper 48 is maintained continuously in contact with the magnet 46 and the core 41 until a set forward force of predetermined strength is applied to the keeper. When sufiicient force has been applied to the keeper to initiate movement of the keeper away from the magnet 46, the keeper quickly moves to the position shown in Fig. 5 or Fig. 6, as the case may be, by reason of the sudden reduction in the force of magnetic attraction applied to the keeper resulting from an increase in the reluctance of the magnetic circuit as an air gap is formed between the keeper and the core. For this reason, the voltage generated within the coil 44 is of sufficient value to fire the detonator 34 whenever the fuze receives a set forward force sufficient to dislodge the keeper 48 from engagement with the core.

whenever the keeper is dislodged from the core as the result of the set forward force received at an angle with respect to the axis of the core such, for example, as when the projectile strikes the target a glancing blow, the keeper is moved to the position shown on Fig. 6 without the necessity of overcoming frictional effects, it being merely necessary for the keeper to be disengaged from the core. The device is thus responsive to a peak force applied thereto, in contradistinction to an impulse comprising a force-time integral of suficient value to move the spring loaded plunger of the prior devices to a firing position with sufficient force to fire a percussion primer. The device of the present invention, therefore, is adapted to be fired by impact of the projectile against a relatively thin plate in which the set forward force applied to the projectile as the projectile strikes the plate is of relatively short duration.

The device, therefore, is adapted to fire the projectile by the peak force of impact of the projectile against a plate of insufiicient thickness to cause the spring loaded plunger of the prior devices to be moved to the firing position with sufficient force to fire the cap or primer. Further-more, the device of the present invention is adapted to fire the projectile as a result of a glancing blow received thereby when theprojectile travels along a relatively fiat trajectory into contact with a relatively level target area by reason of the absence of fric-tion in the forces to be overcome by the set forward force in causing the keeper to be moved away from the core.

On Fig. 7 is shown 'an alternative arrangement in which the fuze is not detonated until the set forward force has been expended sufliciently for the keeper 48 to be moved from an extended position into engagement with the core 41, the firing of the detonator 34, as the keeper moves away from the core to the extended position thereof being prevented by a current rectifying device 52 included within one of the eonduetors 36. As the keeper 48 moves away from the core 41 the voltage generated by the coil 44 is of a polarity such that the flow of current through the detonator 34 is prevented by the reetifying device 52. As the keeper 48 moves toward the core from `an extended position, however, the polarity of the voltage generated by the coil 44 is reversed thereby causingcurrent to flow through the rectifying device 52 by Way of the conductors 36 and thence through the detonating device 34 thereby causing the detonating device to operate and fire the projeetile in time delayed re-` lation With respect to the instant of impact of the projectile against the target. In the arrangement of Fig. 7, it will be noted, the safety Switch 38 is adapted to remain in the open position after the Switch has operated in response to the eentrifugal force applied thereto whereby the short circuit is not reestablished between the pair of eonductors 36 after the projeetile has passed through a plate or come to rest, as the case may be, after being fired.

Whereas in Fig. 4 an arrangement is diselosed in which the electroresponsive detonator 34 causes the main explosive charge t-o be fired simultaneously with the disengagement of the keeper 48 from the core 41, it will, of course, be understood that, if desired, the charge may be fired in delayed time relation With respect to the moment of impact of the projectile against a target by employing an electroresponsive detonating device having incorporated therein a pyrotechnic time delay element, as is well known in the art to Which the present invention relates.

Whereas, the invention has been described in detail with respect to a projectile, it is obviously not so limited as it may also be employed for firing bombs released from an aircraft, rockets, glider bombs, anti-submarine projectiles and similar ordnance devices. Furthermore, although two embodiments of the invention have been illustrated, it is desired to be understood that these illustrations do not exhaust all possible physical embodiments of the invention, and it is desired to be understood that various changes, modifications or additions may be made to the embodiments of the invention illustrated, without departing from the spin't or scope of the invention, except as demanded by the scope of the following claims.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a fuze for projeetile, in eombination, an explosive charge arranged within the projectile, electroresponsive means for detonating the charge, a coil of wire connected to the detonating means, a magnetic circuit within which the coil is arranged, means for setting up magnetic flux within said circuit, a magnetically retained inertia member composed of magnetic material and included within the magnetic circuit, said inertia member being adapted to be moved from an initial position into spaeed adjaceney thereto by a shock impulse and returned to said initial position by magnetic attraction thereby to vary the reluetanee of the magnetic circuit as the projeetile strikcs a target and generate a voltage within the coil sufi'icient to operate said detonating means, and means operatively connected to said coil for preventing operation of said electroresponsive means by the voltage generated in said coil until the inertia member has moved toward said initial position.

2. In a magnetically controlled firing device for an explosive charge, a easing within which the charge is disposed, electroresponsive means for firing said charge, means within said easing for generating electrical power suffieient to operate said firing means, said generating means including a closed magnetic circuit havng a magnetically supported moveable element composed of magnetic material adapted to be moved from an initial position by shock impulse and returned thereto by magnetic attraction and thereby generate said power in response to a predetermined force applied thereto, and means connected to the power generating means for preventing operation of the electroresponsive means as the movable element moves from the initial position toward the moved position and to cause operation of the electroresponsive means as the movable element noves toward said initial position.

3, In a fuze of the character disclosed, the combination of a voltage generating device including a core composed of magnetic material and having an enlarged head thereon, an annular magnet disposed about said core and in engagement with said head, a` coil arranged about the core and within the magnet, an electroresponsive device connected to said coil, a magnetically' supported keeper composed of magnetic material in engagement With the core and said magnet and adapted to be dislodged therefrom by an inertial force applied thereto and returned to said initial position by magnetic attraction when said inertial force has subsided thereby to generate a voltage within the coil sufficient to operate said electroresponsive device, said keeper having the center of gravity thereof arranged such that the inertal force applied thereto in the direction of the 'aXiS of said core necessary to dislodge the keeper from engagement with the core bears a predetermined relation to the inertial force applied to the keeper at an angle With respect to the axis of the core necessary to dislodge the keeper from engagement with the core, and means connected to said electroresponsive device for preventing operation of said electroresponsive means until the keeper moves from its dislodged position to its initial position.

4. In a magnetically controlled firing device for an explosive charge, a easing within which the charge is disposed, electroresponsive means for firing said charge, means within the easing for generating electrical power sufficient to operate said firing means, said generating means including a normally closed magnetic circuit having a magnetically supported movable element composed of magnetic material and adapted to open the circuit as the element is moved from an initial position by an inertial force applied thereto, magnetic means for releasably supporting the element in said initial position, and means for limiting the degree of movement of said element whereby the element is restored by said magnet to said initial position when the inertial force has subsided, and means interposed between said electroresponsive means and electrical generating means for causing the operation of said electroresponsive means as the movable element moves toward said initial position.

5. In a magnetically controlled fuze of the character disclosed, the eombination of a voltage generating device including a magnetically restrained movable inertia element composed of magnetic material, magnetic means for releasably supporting the element in an initial position until dislodged therefrom into spaeed adjacency with respect thereto by an inertial force applied thereto, means for arresting the movement of said 'inertial element whereby the inertia element is brought to rest in a moved position at a predetermined distance from said initial position such that the inertia element is invariably returned to said initial position by said magnetic means when said inertial force has subsided, an electroresponsive detonating device adapted to be operated by the voltage generated by said voltage generating device as the inertia element moves from said moved position toward said initial position, and means for preventing the operation of the electroresponsive device as the inertia element moves from the initial position toward the moved posi- 6. In a magnetically controlled fuze of the character disclosed, in combination, a magnetic circuit including a core, a coil of wire disposed about said core, means for setting up magnetic fiux within said circuit Whereby the coil is adapted to generate a voltage as the reluctance of said magnetic circuit is changed, an inertia element composed of magnetic material normally magnetically retained in engagement with said core and adapted to be disengaged therefrom in response to an inertial force applied thereto, rigid means in normally spaced relationship With said inertia element for fiXedly arresting the movement thereof at a predetermined distance from the core Whereby the inertia element is restored to said initial position only by coaction With said flux setting up means and independently of said movement arresting means, when the inertial force has subsided, an electroresponsive detonating device, and means including a rectifying device for electrically Connecting the electroresponsive device to said coil whereby the electroresponsive device is operated by said voltage as the reluctance of said magnetic circuit is decreased during movenent of said inertia element toward said core.

7. In a fuze for a projectile, in combination, a magnetic circuit, means for setting up a magnetic field within said circuit, a magnetically supported inertia member composed of magnetic material included within the magnetic circuit and adapted for free movement from an initial position to a moved position by inertial force as the projectile strikes a target and to be moved by said magnetic means from said moved position to the initial position when the inertial force has subsided, a coil arranged within said magnetic circuit in linking relation with said field and adapted to generate a voltage having a polarity controlled by the direction of movement of said inertia member, electroresponsive detonating means within said fuze, and means including a rectifying element for electrically Connecting the electroresponsive means to said coil whereby the electroresponsive means is adapted to be operated by voltage received from the coil as the polarity of the voltage is reversed by a reversal in the direction of movement of said inertia member as the inertial force applied thereto subsidies.

8. In a fuze of the character disclosed, a core having an elongated cylindrical portion and an enlarged head portion formed integrally therewith, a circular magnet having an outer tapered surface and a bore therein of greater diameter than the diameter of the elongated cylindrical portion of said core, a nut having a tapered surface engaging the outer surface of said magnet for clamping the magnet to the head of said core and coaxially therewith, a circular coil disposed within and completely filling the annular space between said core and magnet, a cap threadedly connected to said nut and having a bore therein coaxial with the aXis of said core when the cap is threaded on said nut, a conical keeper of less diameter than said last named bore and of less aXial length than the depth of the last named bore for completing a magnetic circuit between said magnet and the end of said core when the keeper is held thereagainst by magnetic attraction, the size of said keeper being just sufficient to permit axial and radial movement thereof Within the cap in response to a force suddenly applied thereto whereby sudden movement of the keeper from an initial position of rest causes a voltage impulse to be generated by said coil.

9. A claim according to claim 8 in which said head portion includes an elongated outlet therethrough opposite said coil and parallel to said axis, and a pair of conductors disposed therein for establishing an external electrical connection to said coil.

10. A claim according to claim 8 in Which said keeper is movable from said initial position in response to a predetermined value of inertial force applied to the fuze.

11. An ordnance fuze comprising, in combination, a magnetic circuit including a core, a coil of wire disposed about said core, a keeper composed of magnetic material and adapted to close said circuit, and means for setting up magnetic flux within said circuit sufi'icient to movably support and maintain the keeper in an initial closed position until dislodged therefrom by a predetermined value of set forward force applied thereto and for magnetically etfecting movement of said keeper from a dislodged position toward said initial position; an electroresponsive detonating device; a firing circuit connected to said electroresponsive device and to said coil; and means in said firing circuit for preventing operation of said electroresponsive device as the keeper is dislodged from said initial position and for causing operation thereof as the keeper moves toward said initial position.

12. In an ordnance fuze, the combination of a voltage generating device including a movably supported inertia element composed of magnetic material, said element being effective upon movement thereof to generate a voltage, means for releasably maintaining the element in an initial position, an electroresponsive device adapted to be operably responsive to the voltage generated by movement of said element, a firing circuit interposed between said voltage generating device and said electroresponsive device and including a unidirectional conductive device for rendering said electroresponsive device insensitive to the voltage generated as said inertia element is moved from said initial position in response to a predetermined force applied thereto.

13. In a fuze for a projectile, in combination, an explosive charge arranged within the projectile, electro responsive means for detonating said charge, a voltage generator within the fuze including -an inertia member composed of magnetic material, said member being of such character as to be magnetically supported by said generator in an initial position and to be returned to said initial position upon dislodgment therefrom, the movement of said member being eifective to generate a voltage sufficient to operate said electroresponsive means, a housing member spatially surrounding' said, inertia member for enabling return of said member from a dislodged position to said initial position thereof, a firing circuit interconnecting said voltage generator and said electroresponsive means, and means in said firing circuit for preventing operation of said electroresponsive means until said inertia member moves toward said initial position after dislodgment thereof.

14. In a fuze for a projectile, in combination, a magnetic circuit, means for setting up a magnetic field within said circuit, an inertia member composed of magnetic material included within the magnetic circuit and adapted to be dislodged from an initial position as the projectile strikes a target and to be returned to said initial position immediately thereafter thereby suddenly varying the reluctance of said magnetic circuit, a cap spatially enclosing said inertia member for limiting the extent of dislodgment and enabling the return of said member to said member to said initial position, a coil arranged to link said field, electroresponsive means connected to the coil and adapted to be operably responsive to the voltage generated therein as the reluctance of said magnetic circuit is suddenly varied, and means for preventing the operation of said electroresponsive means until said inertia member has moved toward said initial position after dislodgment thereof.

References Cited in the file of this patent UNITED STATES PATENTS 384,662 Zalinski June 19, 1888 l,689,470 Adelman Oct. 30, 1928 1,755,023 Buhlemann Apr. 15, 1930 FOREIGN PATENTS 506,280 France May 26, 1920 91,592 Switzerland Feb. 24, 1938 525,333 Great Britain Aug. 27, 1940 

